Apparatus for extruding helical webs on conductors



J. J. NEVlN Nov. 19, 1968 APPARATUS FOR EXTRUDING HELIGAL WEBS ONCONDUCTORS 2 Sheets-Sheet 1 Filed Sept. 28, 1966 IXVLLVIOR. JOHN .1. NEVIN Nov. 19, 1968 J. J. NEVIN 3,411,182

APPARATUS FOR EXTRUDING HELICAL WEBS ON GONDUCTORS Filed Sept. 28, 19662 Sheets-Sheet 2 U\\\ y I 1 w 1 1' 1 1i M N L M [1H1 I 1 I I.

United States Patent M 3,411,182 APPARATUS FOR EXTRUDING HELICAL WEBS ONCONDUCTORS John J. Nevin, Yonkers, N.Y., assignor to Phelps Dodge CopperProducts Corporation, New York, N.Y., a corporation of Delaware FiledSept. 28, 1966, Ser. No. 582,702 5 Claims. (CI. 18-13) ABSTRACT OF THEDISCLOSURE The electrical conductor is passed through the main orificeof an extrusion die having an exit end through which the main orificeopens and also having a sub-orifice intersecting the main orifice andextending generally radially outward therefrom, the sub-orifice openingthrough the exit end of the die with the radially outer portion of thesub-orifice terminating short of the outer periphery of the die. The dieis supported for rotation about the conductor and is provided with aninlet to which a plasticized resinous material is supplied underpressure in all rotational positions of the die, to cause the materialto be extruded continuously through the exit opening of the suborificein the form of a generally radial web on the conductor. Driving meansare provided to rotate the die so as to spiral the web in a helix aboutthe conductor, the pitch of the helical web being determined by therotational speed of the die relative to the speed at which the conductoris moved lengthwise through the die by a transport means.

The disclosure This invention relates to extrusion apparatus and moreparticularly to apparatus for extruding a helical web around and alongthe length of an electrical conductor. A conductor having a web formedin accordance with this invention is useful as a component of electricalcable, such as coaxial cable wherein the helical web serves to maintainthe conductor in concentrically spaced relation to a surrounding outerconductor.

In the past, such helical webs have been formed on conductors by the useof two structurally independent but functionally cooperating elements,one stationary and the other rotatable, which together form theextrusion die. An example of such an apparatus is seen in United StatesPatent No. 2,465,482. In order to provide perfect concentricity anduniformity of the web thus formed, perfect alignment of the two dieelements must be attained and maintained, which is difficult if notimpossible and is time-consuming at best. Modification of the desiredweb, for example, in width or cross section, requires changing one orboth elements and therefore requires a realignment of these elements.

A second known type of apparatus, for forming a helical web about anelectrical conductor, comprises a rotatable die having a cavity wiih theconfiguration of the helix and through which the electrical conductorpasses. In addition to the need for accurately aligning the conductorwithin the cavity, the uniformity of the resulting helix is dependentupon the accuracy with which the die cavity is machined. Furthermore, itis necessary to provide a different die for each different helix pitchwhich is desired. An apparatus of this type may be seen in United StatesPatent No. 2,834,047.

Accordingly it is one object of this invention to provide an improvedextrusion apparatus for forming a uniform helical web about acylindrical element and in which the extrusion die is self centeringwith respect to the element.

Another object of this invention is to provide an extru- 3,411,182Patented Nov. 19, 1968 sion apparatus having sufficient operationflexibility to permit variation in helix pitch without replacement .ofthe extrusion die.

These and other objects and attendant advantages of the presentinvention wi.l become apparent and better understood from the followingdescription and accompanying drawings in which FIGURE 1 is a partiallycutaway perspective view of an electrical coaxial cable produced byapparatus in accordance with this invention;

FIGURE 2 is a schematic illustration of an extrusion system, includingcontrol circuitry, made in accordance with this invention;

FIGURE 3 is a vertical, longitudinal sectional view of the extrusionapparatus of the system of FIGURE 2, and

FIGURE 4 is a sectional view taken along line 44 in FIGURE 3.

Briefly stated, this invention in one form comprises an extrusionapparatus including a feeding means, which may be conventional, fordirecting a plasticized resinous material under pressure to an extrusiondie. The extrusion die is formed with a main orifice adapted toaccommodate passage of the conductor on which the web is to be formed.Intersecting this main orifice and extending radially outwardly from itis a sub-orifice through which the resinous material is extruded. Thissub-orifice, at least where it opens through the exit end of the die,has the shape of the desired cross-section of the helical web,preferably rectangular, with its radially outermost portion terminatingshort of the outer periphery of the die, so that the sub-orifice iscompletely contained within and defined by the die. The extrusion die isheld in a die carrier which is mounted for rotation about the conductorin the main on'fice, and driving means are provide-d to rotate the diecarrier and hence the extrusion die.

In some instances, it may be desired to extrude the helical websimultaneously with an underlying thin film of the material whichcompletely surrounds the conductor and from which the web protrudes. Insuch instances, the main orifice of the die is provided with a diameterwhich exceeds the conductor diameter by twice the desired thickness ofthe film. Otherwise, the diameter of the main orifice is essentially thediameter of the conductor.

The conductor is fed continuously lengthwise to the extrusion die andthrough its main orifice by suitable transport means. In order to formthe helical web about the conductor, the resinous material is extrudedthrough the sub-orifice and the extrusion die is rotated during thislengthwise movement of the conductor. The pitch of the resulting helicalweb is determined by the rotational speed of the die relative to thelinear speed at which the transport means passes the conductor throughthe die, and the pitch can be varied as desired by varying the ratio ofthese two speeds. Because the conductor is supported so that its centralaxis coincides with that of the main orifice in the die, and because thesub-orifice is completely defined by the die, the helical web will beconcentric to the conductor axis and uniform throughout.

Referring now to the drawings, and more particularly FIGURE 1, there isillustrated an air dielectric electrical coaxial cable 8 including anelectrical conductor 10 having a helical web 12 extending radiallytherefrom and formed by the apparatus of this invention. The web servesas a dielectric support to hold the inner conductor 10 concentricallywithin an outer conductor 14.

The term conductor as used herein refers to an electrical conductor ofany conventional material having high conductivity, such as copper oraluminum.

The system as shown in FIGURE 2 includes a payoff reel 18 rotatablysupported by any conventional means, such as jackstands 20, whichpermits free rotation of the reel as the conductor is pulled by anappropriate transport mechanism described below.

The electrical conductor is passed through an extrusion apparatus 22wherein the helical web 12 is extruded onto the conductor 10. Theconductor and web combination is then passed through a conventionalcooling apparatus, such as a water trough 24, wherein the web acquiresits final solid state. Downstream from the cooling apparatus is atransport mechanism for pulling the conductor from the payoff reel 18.Any conventional transport mechanism 26, such as a tractor capstan, maybe employed. The transport mechanism 26 feeds the webbed conductor to atake-up reel 28.

So that the helical web 12 will have a uniform pitch, a coordinatingspeed control 30 is provided which controls the speeds of the transportmechanism 26 and the extrusion apparatus 22. The control 30 is of theknown type which, in response to any increase or decrease in the speedof one, results in a corresponding change in the speed of the other, sothat the relative speeds are maintained essentially constant. Ifdesired, however, the control 30 may be adjusted to maintain a differentratio of the speeds and thus provide a uniform helical web of differentpitch. This adjustment may be effected automatically according to apredetermined pattern, when it is desired to vary the pitch of thehelical web from time to time during a continuous run.

FIGURES 3 and 4 illustrate in detail the extrusion apparatus which formsthe helical web 12. The apparatus includes a block 32 containing acylindrical member 33 and forming therewith an annular cavity 34 forreceiving a plasticized resinous material to be extruded. Anyconventional, nonconductive, thermoplastic or thermosetting material canbe used. The material is supplied by a standard feeding means, such as afeed screw 36, which forces the material through the cavity 34 and intothe adjacent entrance end of an extension die 38.

The die 38 is formed with a central orifice 40 which, as shown, receivesthe conductor 10 with a close sliding fit. Extending radially outwardlyfrom the central orifice 40 is a rectangular sub-orifice 42 throughwhich the res inous material is extruded. The radial dimension of thesub-orifice 42 is slightly larger than the desired Web height in orderto allow for shrinkage when the web 12 cools and solidifies. Theextrusion die 38 is supported within a die carrier 44 and is adapted tobe rotated with this carrier, as through a key 45. The die carrier 44 islocated in a cavity 46 formed in an extension of the stationary block 32and is supported for rotation therein by bearings 48.

In order to provide rotary motion to the die carrier 44 and itsextrusion die 38, a drive sprocket 50 is secured to the die carrier byany conventional means, such as bolts 52. The drive sprocket is adaptedto be driven by a variable speed motor 53 through a suitable connection54.

The electrical conductor 10 is fed through a guide 56 centrally locatedwithin the cylindrical member 33 and passes from this guide through thecentral orifice 40 in the extrusion die 38. The die 38 has a conicalcavity 39 tapering from the entrance end of the die toward its exit endand forming an inlet to the orifices 40 and 42. The guide 56 has asimilarly tapered end 57 centrally located in the die cavity 39, so thatthe extrusion material is forced from the annular cavity 34 through thetapering annular passage surrounding the guide end 57, and thencethrough the sub-orifice 42.

In forming the helical web 12, the conductor 10 is pulled lengthwisethrough the extrusion die 38 by means of the transport mechanism 26.Simultaneously, the resinous material is fed by a screw 36 to theextrusion die 38 and is extruded through the sub-orifice 42 in the formof a radial web having its inner edge in contact with the conductor,since this sub-orifice intersects the main orifice 40 through which theconductor passes. At the same time, the extrusion die 38 is rotated bythe variable speed motor 53, resulting in the formation of a uniformextruded web 12 spiralling about the conductor 10 along its length. Thespacing of the convolutions of the helix, that is, the pitch of thehelix, is determined by the speed at which the conductor 10 is movedthrough the die 38 and the speed at which the die is rotated. With afixed speed of conductor movement, an increase in rotational speed ofthe die decreases the helix pitch. Conversely, with a fixed rotationalspeed of the die, an increase in speed of conductor movement increasesthe helix pitch. Accordingly, the coordinating speed control means 30can be programed to provide any desired pitch by merely adjusting therelative speeds of the transport mechanism 26 and motor 53. It is alsonecessary to control the rate of material feed in order to insureuniformity in web thickness. For example, if the conductor movement orthe die rotation decreases considerably in speed, it is necessary tosimilarly decrease the rotational speed of feed screw 36 in order toavoid feeding the material at an excessive rate to the extrusion orifice42. The speed control of the feed screw 36 is coordinated with theoperation of the transport mechanism 26 and variable speed motor 53 bymeans of the speed control means 30.

Any desired web shape can be provided by merely varying thecross-sectional shape of the extrusion orifice 42. Similarly, varioussize conductors can be accommodated by interchanging the extrusion die38. This is accomplished by merely removing the die carrier 44 from theblock 32 and replacing the extrusion die 38 with the appropriate die.The die and carrier assembly are then reinserted in the cavity 46. i

As will be observed from FIGURES 3 and 4, the extrusion is effectedthrough an orifice 42 extending radially outward from the main orifice40 but terminating short of the outer periphery of the die 38, so thatthe extrusion orifice 42 is defined entirely by the die and theconductor 10 passing through the main orifice. Consequently, it isunnecessary to center the extrusion die 38 with any other element of theapparatus, in order to form a uniform helical web 12 which is perfectlyconcentric to the conductor 10. Such concentricity is assured simply bypreventing lateral movement of the conductor relative to the mainorifice 40, which movement is avoided by a close sliding fit of theconductor in the orifice or, when the aforementioned thin film is alsoto be extruded, by the centering action of the resinous material as itis forced through the annular tapered inlet 39 surrounding theconductor. In other words, the present apparatus is entirelyself-centering for the purpose of maintaining the helical web concentricto the conductor. Moreover, the helical web is formed without resort toa helical die cavity, which requires accurate and difiicult machiningand limits the helix to a predetermined pitch.

The extrusion material supplied by the feed screw 36 may be any of thepolyolefins, cross-linked or not, such as polyethylene, polysulfone orTeflon. The cooling apparatus 24 serves to solidify the extrudedmaterial before it is engaged by the transport mechanism 26 which pullsthe conductor from the extrusion die.

I claim:

1. Apparatus for extruding a helical web along the length of anelectrical conductor, said apparatus comprising (a) an extrusion dieformed with a main orifice through which said conductor is adapted topass, the die having an outer periphery and also having an exit endthrough which said main orifice opens, the die also being formed with asub-orifice intersecting said main orifice and extending generallyradially outward from said main orifice, said sub-orifice openingthrough said exit end of the die with the radially outer portion of thesub-orifice terminating short of said outer periphery, the die formingan inlet to said sub-orifice,

(b) means supporting the die for rotation about said conductor in themain orifice,

(c) means for supplying plasticized resinous material under pressure tosaid inlet in all rotational positions of the die, to cause saidmaterial to be extruded continuously through said exit opening of thesuborifice in the form of a generally radial web on the conductor,

(d) transport means for moving said conductor lengthwise through saidmain orifice, to draw the extruded material from said exit end of thedie, and

(2) driving means for rotating the die in one direction about saidconductor to spiral the web in a helix around the conductor, the pitchof the helical web being determined by the rotational speed of the dierelative to the speed at which the conductor is moved lengthwise by saidtransport means, and the radial dimension of the helical web beingdetermined by said sub-orifice within the die.

2. Apparatus as defined in claim 1, in which the die has a conicalcavity tapering toward said exit end and forming said inlet to thesub-orifice, the apparatus comprising also a stationary guide memberhaving a conical end disposed in said cavity in spaced relation to thedie and tapering toward said exit end, said member having a passage forguiding the conductor to the die and opening through said tapered end,said material supplying means forming an annular supply passagesurrounding the guide member and opening into said cavity at the end ofthe die remote from said exit end.

3. Apparatus as defined in claim 1, comprising also control meansoperatively connected to said driving means and said transport means formaintaining a predetermined ratio of the rotational speed of the die andsaid lengthwise speed of the conductor.

4. Apparatus as defined in claim 1, in which said main orifice isdimensioned to receive the conductor with a close I sliding fit.

5. Apparatus as defined in claim 1, in which said transport meansinclude mechanism for pulling the conductor from the extrusion die, theapparatus comprising also cooling means interposed between the extrusiondie and said pulling means and operable to solidify said extrudedmaterial on the conductor.

References Cited UNITED STATES PATENTS 2,446,057 7/1948 Morin 18l3 RXR2,805,179 9/1957 Burr 1813 RXR 2,834,047 5/1958 Morin 18-13 R WILLIAM J.STEPHENSON, Primary Examiner.

